The map is wrong. The mountain made it that way. And somebody used it to kill a man.

Silas Thorne measures the world for a living. His partner Linus reads the men who own it. Together they take the commissions other surveyors won't touch—the plats that don't close, the claims that move overnight, the boundaries drawn by men with a reason to be off by a degree.

Four years of following a dead man's errors have brought Silas to a gate in the Sierra: a fifty-yard notch in a wall of red iron hills, and behind it a valley his father surveyed and then deliberately cut into four pieces so that no one could ever assemble it.

The people of that valley let him through for one reason. Their factor is dead.

Simón Arriaga walked the outer road for twenty years—salt in, hides out—and never once mistook a sound roof for a rotten one. Now he lies under a collapsed adit on a claim jumped this spring by a company with every legal paper in order and no honest business being there. The camp calls it a rockfall. Nobody in Cinabrio wants to call it anything else.

Silas has three things the camp doesn't. A theodolite. A claim book with one line re-inked. And a needle that swings a degree and a half west of true every time he sets it down on red rock.

Every survey in the district was measured against a north that does not exist. Someone knew it. Someone built on it. And someone killed a man to keep it standing.

To name the killer, Silas and Linus will have to demonstrate the mountain's lie in daylight, in front of two dozen armed men who profited by believing it—and then decide what a stranger owes a country that opened its gate to him exactly once.

The False North is the ninth mystery in the Thorne & Linus Cartographic Mysteries, a historical detective series for readers who like their crimes solved with instruments instead of revolvers. Each book stands on its own.